In such apparatus the central shaft or ram rod is axially guided in the hollow drill spindle, and at least one coupling element is provided for connecting the drill chuck to the drill spindle. The coupling element can be arranged, on the one hand, in retainers of the drill spindle, and in retainers in the chuck body of the drill chuck, on the other hand. As a function of its setting, the coupling element, however, will allow an axial clearance, play or displacement of the chuck body with respect to the drill spindle, and this can be selectively set and terminated by a locking mechanism having a coupling ring.
The German patent publication DOS No. 34 13 581 which may not be prior art hereto,(see the aforementioned list of earlier applications), discloses a percussion drill in which the locking mechanism is a contact ring which is arranged on the drill spindle so that it can rotate or turn, but which is fixed when considered axially or longitudinally. The contact ring is arranged axially opposite along an annular shoulder of the drill spindle, and it carries abutment or contact projections which are directed towards the annular shoulder and which preclude the axial shifting or displacement of the drill chuck on the drill spindle when they come into contact with the spindle shoulder, i.e. the annular surface thereof.
The annular surface of the annular shoulder includes abutment recesses into which the abutment projections can reach, and the depth of these abutment recesses is at least equivalent to the magnitude of the permitted axial displacement or play of the drill chuck. Accordingly, when the contact ring is turned such that the abutment projections are in alignment with the recesses and the projections can enter into the respective recesses, the axial shifting is possible, i.e. the mode of operating with axial chuck play is established.
It follows that the drill spindle must be provided with abutment recesses which are adapted in size to the abutment projections of the chuck that is being used. Furthermore, the mentioned locking mechanism is primarily intended for such impact drills in which the axial displacement is of relatively minor magnitude, i.e. only a minor stroke or displacement distance is provided.
However, when a chuck is to carry out a large stroke, for example, as large as that of the drill, in the mentioned locking mechanism the size of the chuck is increased in approximate conformity with the magnitude of the stroke of the attendant movements. Finally, in the mentioned percussion drill inherently undesirable operational conditions may arise in that during the percussion operations with the mode with axial displacement or play, the lock ring is not locked, or when the axial displacement mode is not used, during normal drilling, the control ring is blocked, i.e. it can then not be used for clamping or tightening a drill.